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This 300 seat church already had a reasonable high-quality sound system. It was properly designed for the room and professionally installed. The acoustics were not that bad. At least it was thought that the acoustics were not such a problem. The outstanding issues they were trying to solve or improve were:

Gain before feedback,

Elimination of the few deadspots that were not solved from the previous sound system when the current new JBL speakers were installed

Reduce sound spill from floor monitors,

Better control of the drums (when using acoustic drums) and

They wanted 3dB more bass from the Sub-woofer.

These are all reasonable reasons to upgrade the sound system.

The church was considered the following upgrades.

Replacing the professionally designed and installed 12-year-old JBL sound system.

They considered going for IEM (in-ear monitor) system for up to 8 people. (This would have included a new digital mixer)

The church considered making an air-conditioned drum booth or get an electronic drum kit.

They also wanted to add a second twin 15-inch sub-woofer.

Estimated total cost, almost $26,000.00 installed.

This is what the church actually did. They changed the acoustics of the room. They installed an acoustical Tube Radiator system.

What did they gain by doing this?

The sonic quality of the existing JBL speaker system was greatly improved. The improvement was noticeable better regardless of how much equalization was added or when the EQ was bypassed. (Definite proof that the acoustics of the room changed the performance of the speaker system from the day they were installed.)

All of the remaining deadspots were now gone. (This was never a speaker system problem as the right speaker system design was already installed.)

The performance of the speaker system was such that picking up a person’s voice went from 12 inches to 35 inches with a Shure SM58 mic before feedback would show up. (Again, acoustics limits the performance of all sound system. Sure there are some very expensive gadgets that can improve gain before feedback, but such gadget can cost more than the material cost of the acoustical fix.)

The floor monitors are now well behaved. No matter how loud the floor monitors get, you definitely need to and to add the front of house to hear clear sound. As it turns out, the overall stage mix dropped around 10dB without the performers even noticing as they were now able to hear the stage mix from the monitors so well at a lower volume. You could say that the monitor spill issue is eliminated.

This eliminated the need for IEM’s.

Since the drummer can hear himself now, he gradually started playing quieter after a few weeks. The need for a drum cage disappeared.

The Single Sub-Woofer was now able to play 9dB louder without distortion. It would have taken 3 more sub-woofers to get the same loudness without distortion. That was equal to spending around $15,000.00. (Standing waves and bass buildup in the corners added air pressure onto the surface of the cones of the subs drivers. This added air pressure creates distortion. When the subs distort, the sound quality and maximum sound levels of what the sub is supposed to be able to do, can drop up to 15dB in many rooms.)

Other improvements

Congregation Singing.

The participation of people singing went up from 30% to 75%. (When people can hear themselves and the other people around them, it encourages people to sing more.) s a resulting, the congregation is singing 8 to 15dB louder. (The more people singing, the louder they will become.)

No more distortion from the speaker system with playing louder which means the perception of loudness is greatly reduced. (Standing waves and bass buildup in the corners added air pressure onto the surface of the cones of the bass driver of full range speakers. This added air pressure creates distortion. When the bass drivers distort, the sound quality and maximum sound levels of what the full range speaker is supposed to be able to do, can drop up to 15dB in many rooms.)

After two years, the congregation is starting to add harmonies to their singing. (That is what happens when people can hear each other.)

Now when people stand up to give testimonies or prayer requests, people can hear them whenever they forget to use hand-held wireless audience microphone.

The front of house stage mix is so much better. Now you can hear all of the performers without having to blast the sound system. (A well-diffused room can make the signal to noise ratio improve from 3dB to 25dB. As the signal to noise improves, the easier it is to settle into a high quality.)

The worship space is now concert quality for any high SPL event, recitals, choirs or orchestral events.

The total cost of the acoustical system including painting the whole sanctuary. $1,400.00
Since this as a DIY project, the money saved went towards a better headset mic for the pastor and the new digital mixer. Total upgrade, $5,000.00. If the church contract out the installation of the Sono Tubes, add $5,200.00. That is still 60% of the cost of upgrading a perfectly good sound system if everything is contracted out or an 83% difference.

Conclusion

One can honestly say that fixing the acoustics had a far better return on investment versus just upgrading the speaker system alone. Upgrading the speaker system can never make the room sound better, improve congregational singing and it would have not been possible to delete the deadspots without adding more speakers on delays around the room. This transformation is typical of the new worship experience when a church gets the acoustics they are supposed to have. In the battle between acoustics vs sound systems, acoustics always wins. It’s Physics. Try moving a wall with air? You can’t. Change the wall and hear what happens!

An unwelcomed guest in any church is Mr. Deadspots. Unfortunately, deadspots in churches are more common than you think. There are two main types of deadspots. Some are frequency related/comb filtering interference and others are dips in sound levels greater that 6dB created by the room.

It is common to see frequency related deadspots in Left/Right sound system regardless if they are Line Arrays or point and shoot speakers. These deadspots are created by interference patterns in a mono speech system as a persons voice is always mono. These deadspots are where you shift from one foot to another and notice a sound change. In these cases it becomes a problem when on one foot you hear the highs but not the lows. When you shift your position onto the other foot, you hear the lows and the highs disappear. People with hearing aids or early stages of hearing lose notice this the most. People with good hearing notice the change too but learn quickly to put up with it. Some young people think of it as a passive noise filter. If the music is too bright, stand to one side of your seating position. If the music is too boomy, shift to the other side of your seating position. Really! Isn’t that like buying a headset and controlling the sound changes with what angle you tilt your head. It might sound like a great idea until you find yourself with a lot of neck pain. No thank you.

Sound level dips are usually acoustically related. These are created with standing waves, bass building up, hollow walls, room corners, and parallel surfaces that include walls, ceilings and floors and concaved surfaces. In all of these cases, often mid and bass energy build up and the highs are absorbed with carpets, padded pews and people. By the nature of churches and how they are used, carpeted floors and padded seating often represents how the church sounds when it is 50% full. That means that if your attendance is often over 50%, the effects of padded seating and carpeted floors has little to no impact. If church attendance is often over 70% a carpeted floor makes the room more intimate during times of prayer and solemn reverence. In the end, carpets and padded seating is a good thing.

However, because of people in the room, once that room attendance is above 50% the people absorb enough highs that extra mids and bass energy is left behind as is being amplified between parallel surfaces. This excess energy automatically masks the highs. When the highs are masked, speech and music intelligibility drops. The kicker is, if you go around the room with a sound level meter, often the sound levels don’t drop much, even when you stand in a spot where the highs (when you measure just the highs) drop off over 6dB. That is because the excess bass energy is so strong that it fools the sound meter as the meter is reading an average sound level. When you take sound level readings by frequency, then you notice the high number of deadspots in the room. Get a tone generator in a cell phone or computer app and play a constant tone at 55dB at 500 Hertz, 1000 Hertz and 3000 Hertz and then start walking around. At 500 Hertz you shouldn’t notice much of change until you get close to walls. At 1000 Hertz you will notice more changes. At 3000 Hertz, if you are hearing a lot of changes, imagine what 25% of your church audience is experiencing.

Here is a church that had both acoustical and sound system created deadspots, with a central cluster. By nature of a central cluster, in a good room, it gives the best coverage and performance for speech. There is no better way to design a church sound system unless your ceiling is less than 14 ft. high. Choice of speakers, coverage patterns and speaker placement impacts sound too but these are mainly tone qualities and gain before feedback related. It may have up to a 2 or 3% impact on overall intelligibility as well.

In this church example, it already has a fairly good quality speaker system in the ideal location for the room. It is designed as a central cluster and by nature, in this setup, it should perform well. However, it didn’t matter if you used the main speaker system or used portable speakers on stands, with any sound amplified you could find deadspots all over the room. On top of that, if you raised your voice in the room, once you were more than 18 feet from someone, understand what was being said was difficult to impossible depending on dictions of the person talking and how good is one’s hearing. When the proper acoustical fix was applied, all of those problems went away and the church didn’t need to upgrade the speaker system.

The church decided to leave the sound system alone as the gain before feedback improved and all of the deadspots disappeared. Since this is a traditional church that has no intentions to do anything contemporary, the acoustical fix was designed to not change the overall reverb time. Before and after reverb time remained about the same. 1.7 seconds. It was the frequency response of the room that saw a major change. As the graphs shows below, where the mixer for the worship space was located, it was also one of many spots where weird measurements were recorded before. We found dozens of spots where the room measurements went squirrely. This is typical of the results of measuring a Left/Right speaker system, not a cluster system. These weird results were a result of room acoustics and not the sound system. We used our own test speaker for all room testing.

After checking our test equipment for errors, it was then realized that by just moving the mic over a few inches, you would get a very different result. In some places, the sound was perfectly fine but move over a few inches and it was not. Our ears are about 8 inches apart. In one row of seating, the largest distance we could move the test mic between a good spot and bad spot was 14 inches. Pew seating is 18 inches. Every seating position had both good and bad sound. What we were measuring was sound masking in the mids and lows. The energy was so strong that it masked the highs. Not only that but the highs were most likely also being canceled from nearby wall reflection between 1800 to 5000 Hertz. It gave the impression that there was something wrong with the sound system.

In this church, people marked their seating positions by placing personal pillows in spots where the sound was better. Sure enough, testing these spots showed better sound before the acoustical treatment was applied. After the acoustical system was installed, the sound was the same no matter where you sat including the sound booth.

Deadspots in churches are more often a result of worship space design and not a result of sound system design (unless you have the wrong speaker system design for your room). When a church replaces a well-designed sound within 10 years, and have little to no overall improvement after an upgrade, that should be a BIG RED FLAG that you most likely have a serious acoustical problem and no amount of money spent on the sound system can make those problems go away. Besides, these days, acoustical fixes cost less than sound system fixes. As a caveat, our experience has been this. Churches that have fixed their acoustics and then wanted on to expand their music programs, they were able to upscale their sound system with a much higher budget as they upgraded, it actually lead to better performance rather than an exchange of one set of problems for another.

Bottom line is, get your church properly tested. Have someone who knows how to properly diagnose the data, and then design your church a proper acoustical management system. Install the acoustical system and watch the congregation respond and grow. Don’t be surprised if other churches want to use your church for musical and recording events. Your property value may go up too.

Note – The acoustical system is made up of 8 and 12 inch half round plaster covered foam diffusers on 3 walls. The side walls use a gradient pattern to maximize room performance. On the back wall there are 24 units of 7 ft. x 2 ft. x 18 inch plaster covered foam diffusers that are hollow which allows for additional passive room equalizing in the near future. Project completed by church members.

There are dozens of acoustical spreadsheets that come with the promise of a viable acoustical fix. Some sheets are for studios and some are for home theatres. There are also other spreadsheets for larger rooms. As rooms get larger, (as in Christian Churches and worship centers) those spreadsheets become less accurate. Sure, the better spreadsheets adds more variable to compensate for the limitations, but the limitations are still there. Furthermore, with all of the spreadsheets, you have to add an additional line to include a fudge factor. In some spreadsheets you need to add multiple fudge factor lines.

When a person tries to use an acoustical spreadsheet, they are only looking at one parameter of the rooms acoustics. You are only looking at “time.” The problem is, for churches, and I MEAN ALL ROOMS WHERE MORE THAN 150 PEOPLE GATHER TO WORSHIP – there are other parameters that are equally or more important than “time.” Acoustical problems always come in layers. The minimum number of layers of acoustical sound management in a worship space is 4 layers. As a worship space becomes larger, the more layers you have to attend to. “Time” becomes only a fraction of the real acoustical problems you are faced with. Obviously you can’t see them but you can measure them if you are trained to recognize when you hear them.

The problem with spreadsheets is that they are not looking issues such as standing waves – and every church – regardless of shape has standing waves (unless the space is acoustically managed in the first place which also means this article is not for you.) Spreadsheets are not looking at excessive noise from early and late reflections. They are not looking at bass buildup often found in the corners of a room. They are not looking at flutter echoes and full syllable echoes. These are all sound effects than can’t be dialed out with equalizers, delays, algorithms and the next miracle digital gadget or software. (Yet that is how most sound system designers try to deal with room acoustics.)

Regardless of a persons acoustical training, knowledge or experience, a spreadsheet cannot tell you when standing waves are masking flutter echoes. A spreadsheet cannot tell you when bass build up is masking a standing wave issue. A spreadsheet can’t tell you how much the early and later reflections are reducing music and speech intelligibility.

All that a spreadsheet can tell you is how much “time” it takes for a sound to decay in a room either as an average number. Some spreadsheets are much more detailed and they have been written as an attempt to calculate a room in octaves or by 1/3rd octaves. If it was only that easy. Measuring and calculating time is just a sliver of the acoustical signature of a space people worship in.

It takes a lot of training to learn Church acoustics. The same applies to Studio Acoustics, Recital Halls, Concert halls and lecture halls. All of these rooms have specific acoustical needs and they all require a unique set of skills to properly fix them.

What makes a church so complicated is in how a church is used. When a church is designed as a “church,” it becomes the most multipurpose space there is because of all the ways a worship space is used. When you say you want the worship space to be more “Multi-Purpose” or more flexible in it use, you are actually limiting what a basic worship space is supposed to be able to do.

At the end of the day, an acoustical spreadsheet is only a small snapshot into church acoustics. It can’t help with congregational singing, it can’t help with a noisy stage for a praise and worship team or choir and it can’t help with drum issues or speech intelligibility.

What often happens is with the spreadsheet, it will guide you to a solution that is based on absorption. When an acoustical fix is based around absorption, you wind up “killing” the room for all music – especially contemporary music and congregational singing – and the masking effects of the other acoustical issues get worse. Sure, the room sounds more tame than it was before, but the ability to understand speech is either no better than before or it has gotten worse. Before you know it, everyone gets in ear monitors and all of the members of the worship team have to sign an insurance liability waver stating that they will not sue the church for any future health problems with hearing loss. Seriously, is that the kind of acoustical fix you want?

That is what you get when you turn to an acoustical solution based only on spreadsheet calculations. To top it all off, the results are not much better when using computer simulation software programs. Simulation programs only show you the results at one frequency at a time. The computer generated image may be 3D but the patterns they show are only one frequency at a time – even when it is averaged out. To see large room acoustics in a simulation, you need to be able to see the results in 4D. Hologram can’t show you 4D images. That ability hasn’t been invented yet. You need to be able to see sound in 4 dimensions because all sounds are complex. Every sound made on earth is a combination of wave lengths that are generated at the same time. Some parts of a sound are measured in feet and some in inches. There is no way to visually see 100 Hertz, which is 11 ft long, and 4000 Hertz which is 3.5 inches long, at the same time in the same place yet in real life, that is what is happening with sound. We all take sound for granted but the complexity of sound is extensive.

But doesn’t sound follow the rules of fluid dynamic and other laws of physics? Of course it does, but only when you examine one frequency at a time and that frequency is never a pure tone. It is always complex. The only place you can measure and see a pure tone is in a machine like an oscilloscope and the moment you launch that sound into the air, it becomes complex. Just as sound is complex, so are the acoustical fixes for churches.

This is one way to test an acoustical solution before you recommend it to a church. Have your own testing facility. Whatever research is done in this room, it mathematical translates perfectly when it is scaled up into a larger space.

As a mantra, remember this: for all Christian churches, acoustical problems come in layers and whatever fix you choose, it has to address all of the layers in one step – which is possible if you want an affordable fix. There are many tools in the Acousticians Tool Box to fix a worship space. There are diffusers, resonators, traps and other devices that can address the needs of a church’s acoustics. There are also stand-alone electronic solutions that work in certain worship spaces. You need a lot of training to know which ones you need, what combinations you need and how to use them, and the last place you want to do your training and experimenting is on your customers.

If you are doing Church Acoustics or trying to fix your own church, don’t do it as an experiment and you know it will be an experiment the moment someone in your committee say something like, “lets try this as see what happens.” With those words, the acoustical solution is already doomed. Experts like myself can tell you the results the second you decide to try something and long before you apply the materials.

History shows that after a church spends it’s money on a thing such as acoustics, it will not be able to afford to fix any mistakes for decades. If the results makes the room worse or no better than before, then you are subjecting the church members to more sound abuse for years to come and we don’t want that. Spreadsheets don’t fix churches, good training and expert help does. (It’s also cheaper in the end to get expert help.)

Finally, consider this. The internet has become a treasure trove of knowledge. That knowledge is often presented as expert information offering sure fire solutions. I scan the internet often to see what is out there. There is a lot of great information and there are a lot of myths. When you collect all of that info, it only holds a fraction of the total knowledge about church acoustics. If we were to put a percentage on it, the internet holds about 2% of the total knowledge there is for church acoustics. The books hold another 8% of what there is to know about church acoustics. Church acoustics is so complicated that often, a seasoned acoustical expert like myself will have to fix one of a kind acoustical fixes often. Those unique fixes are often not shared because others may think that the one of a kind fix would be needed in every other church that has the same problem. You can have 10 churches with the same acoustical problem but in every one the fix has to be modified because of the other variables that have to be included. The rest of the knowledge about church acoustics is held by experts because the church community hasn’t taken ownership of that knowledge yet and there is no system in place for churches to share their experiences in order to avoid mistakes in the future. What is missing is the wisdomin knowing what acoustical fixes will enhance worship verse what acoustical fixes exchanges one set of problems for another set of problems. Problems which holds back and undermines the real worship experience the church leaders want you to participate in.

All church can have great acoustics and sound. If each church denomination or independent church were to set-up their own “Church Sound Standards” for the performance of their sound systems and worships space acoustics, churches will become the kind of places where people want to go. Once a standard is set, every church will have a Worship everyone can enjoy and appreciate.

If you are in a new church building or you have done major renovations in your church, you will have to re-equalize the sound system many times in the first few years. Here is the Schedule you should follow.

First year – After the 1st month, 3rd month, 6th month, 9th month and 12th month

Second year – After the 4th month, 8th month and 12th month.

Third year – same as year 2

Fourth year – after the 6th and 12 month.

Fifth year – same as year 4

Sixth to tenth year, every 8 month.

After that, once a year.

It take up to ten years for most building to fully cure or longer depending on how much concrete and wood is used. For that reason, the humidity of the church becomes lower and lower as the church ages which also changes the sound of the worship space.

Also, depending on the climate area you are in, you should be re-equalizing your church sound system for each season. more so the further you are from the equator. If you have a digital processor or mixer, you can have presets for the room changes.

Well, it finally happened to me. After warning other people for years to use a Direct Box when connecting to a sound system, what did I do, connected an IPad to a mixer with an adaptor from 1/8th stereo to 2 channels of Balanced outs. Then boom, the IPad headphone output was fried. How? The mixer had global Phantom power on all of the channels and because I went into the balanced inputs rather than line level 1/4 inch inputs, the voltage of the phantom power fried the IPad.

When I brought my IPad in for repairs, fortunately it was just the headset circuit that was damaged. The owner of the repair store said that he had seen this problem before with other IPads, computers, portable CD players and cell phones. With one person, their IPad was so damaged that the IPad had to have the main board repaired too. Ouch.

Fortunately, there are a few direct boxes you can use that are purpose made for connecting from consumer to pro audio equipment. What you want is a direct box that will give you 1/8th stereo and RCA two channel input to two channel stereo outputs via XLR’s. Some model have a switch for stereo or mono outputs. Pad switches and ground lifts are a must as well.

On this project we were firing up the speaker system for the first time. I needed stereo output and we used an older mixer that was in storage. We hooked up to two channel and we were outputting to stereo (even though this will be a mono system.) OK, I wanted to impress the people who were in the room at the time. The demo and initial speaker setup was a great success but I happened to remove the connections from the mixer while the mixer was still on. Not sure if the unplugging or the circuit that was heated up so much that when it cooled, it came apart that signed the connection failure but the next time I turned on my IPad to hear something, it would not work.

Either way, whether you are using a PC, Laptop, Cell phone, IPad, IPod or any consumer product that has 1/8 or RCA outputs, get a proper Direct box. They range in price from $69 to $160. That is cheap insurance considering that fixing my IPad cost about $100.00 and 7 days to get the parts to repair it.

For sound quality and extra insurance, get DI boxes that have transformers on the input or output side.

Apparently it is true. At a recent church meeting where a 160 year old Roman Catholic Church is being restored, the acoustical treatment that I designed will also help to preserve the walls behind it. The acoustical panel will carry current and future artwork while the walls behind the acoustical system will be sealed. With no paint going onto the walls, the existing brick and concrete will no longer be degraded by the chemicals in the paint. This could be the first time where acoustics, Church Iconic Art and preservation are combined together. According to the restoration company, this approach could double or even triple the cycle between major restorations. The church has already been partially treated for sound acoustics and the improvements have convinced church leaders that the rest of the room should be treated as well. For this church, no absorption is being added. Only diffusion is being added to create a phase coherent worship space. The restoration company thinks that adding acoustical treatment system an affordable way to extend the cost of the restoration and it will give better results for hearing and the sound system performance.

Get your hearing tested for free. If you have an iPad, iPod or iPhone, you can test your hearing with a free App. It is good enough to confirm whether if you have a hearing problem and whether you should be getting professional help.

The software is from Unitron and they make hearing aids. So while some people think that this is just a sales marketing tool, and it very well may be, but it matches a hearing test of mine done in a proper lab hours apart. That is good enough to decide who should be behind a mixer and making adjustments during worship.

What I have also done is use this test for people who persistently ask me to turn things up – even when they have sat in different places. When everything is working properly and I know the sound system is passing the STI speech intelligibility test, I will ask the person to take the test. Be gentle and kind when asking people to take the test. When people discover that they need help, setting them off in getting their hearing back often gives them back their life too. The App is called “U-Hear”

If experiencing poor sound in church could be measured as pain and people are not complaining about it, it could be because they don’t consider taking 10 extra strength pain killers per worship service as overdosing.

Is your sound system making the right impression? Are the acoustics of your church allowing your sound system to make that great first, second and third impression at your church?

Once again the subject of getting more performance out of the next sound system upgrade keeps coming up. When a church is constantly seeking to get more performance out of a sound system at every upgrade and not be enjoying the best sound possible then it’s time to fix the room instead of putting it off and investing into more equipment. This is the message your sound system is broadcasting. Are you listening or are you waiting for the next technology breakthrough for that sliver of improvement?

Direct Boxes

This information has be written for the layman and should not be used as technical information. Many terms and descriptions are simplified for educational reading.

Thank you.

What are they and why do we need them?

It’s 10:00am Sunday morning. The invited Gospel group just showed up an hour late. You have 45 minutes to set up, do a sound check and rehearse the group long enough to know what kind of sound they are best known for.

One by one the performers enter with their instruments. This group is planning to use the church sound system. Rumor told them that this church had a very good system. You see one electronic organ, two electronic keyboards, one string bass with a pickup and one electric guitar with an amplifier head. Finally, you see an electronic drum kit.

At the front of the church you have 16 mic inputs. You need 5 vocal mics and 9 inputs for the instruments. That leaves you with a pulpit mic and a tape player input.

By 10:30, the sound check was finished with the soundman sitting at his mixer in the pew and 10 minutes later the group finished their rehearsal and floor monitor check. At 11:00am, service started and the group performed very well. Most people were not aware that the group set up in only 45 minutes. Is this really possible? Ever since the 16mm film projector was used in the church and connected to the sound system, churches have needed a direct box (or DI box). DI boxes are used to change the output signal from one source and change the level and impedance to match a microphone level signal input into a mixer. The most common application of a direct box is when connecting an electronic keyboard or similar electronics to a sound system. The DI box allows you to connect into a snake or existing mic lines and send the signal up to 700 or 800 feet away. By converting line level signal to a balanced signal mic level, you also avoid RF problems and crosstalk in the mic cables back to the mixer.

There are 5 quick and convenient type of boxes

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Passive Direct Box

The most common DI box is the Passive Direct Box. This unit is often used to connect Guitars, Keyboards and other electronics that have a line level out from the instrument. Often the line level voltage is between .5 volts to 3 volts (Some DI’s units can handle an input signal of +8dB (or 10 volts)). As a passive unit, the signal is as good as the transformer that is built within it. An important feature of many good quality DI boxes is ground lifting. Since there is no universal standard for audio equipment and instruments, grounding problems often occur (Perhaps the new ISO9000 standard may help…. but let’s see what happens in the next few years.) Many DI boxes are able to isolate grounding problems between various items of equipment. Generally, by going through a DI, you loss from 3 to 6dB of signal.

** Note: Not all DI boxes sound the same. As the signal levels get higher, the DI box may add some distortion. On an electric Guitar it may be a good thing. On a Keyboard it can sound awful. Before you blame the soundman for that poor keyboard or instrument mix in the monitors, try a different DI box or even an Active box.

Active Direct Box

The second most common DI box is the Active Direct Box. These units either work from a battery or phantom power from a mixer. An active DI box can handle higher signal levels and put out a higher signal level. Furthermore, the frequency response is often better too. When you are performing in a room that has low reverberation and good performance qualities, it is better to use the active DI box. Also if you plan to use a digital signal in reinforcement or recording, use the active DI box. Generally, a DI has 0dB signal loss.

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Active Direct Box with Preamp.

A new type of Direct Box may have a built in preamp that works off the Phantom power of a mixer or it might have batteries or it might have an AC/DC adapter. I haven’t had a chance to test one, but the are supposed to boost a signal level up to 10dB. Some of these units can also work as a mic preamp as well but that is only when your mixer dies and you need 1 mic to get through the show. But that would only work if you have a box that is self powered or with an AC adapter.

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Speaker Director Box

The less common DI box is called the Speaker Director Box. A speaker director is used when the only signal output available is from an amplifier. Many older 16mm film projectors use a 10 watt tube amplifier for driving a 10 watt speaker. A tube amplifier should always have a nominal load of 4 ohms or higher on the output or the amplifier will burn itself out. A good speaker director will present to the amplifier a proper load and convert the signal to mic levels to either a 150 or 600 ohms. You should never take a signal from an amplifier direct into a mixer. You will either fry the channel or the power supply in your mixer.

Remember, all good direct boxes have ground lift switches and there are a few units that have an automatic grounding system. Make sure that your direct box has this feature.

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Line Matching Transformer

Another common method of connecting low level electronics to a sound system is by using a line matching transformer. The transformer is usually mounted in a barrel type connector with a ¼ inch-tip sleeve connector at one end and an XLR three pin connector on the other end. The whole unit is often about 4 inches long. There are only a few manufacturers of these products and they seem to work.

Radio Shack, EV and other mic companies has two types and churches tend to buy these because they are so visible and easy to get. One converts low level line outputs to mic levels. This unit with the ¼” female to male XLR can handle a lot of power but, there is a major penalty when you drive this transformer to hard. In bench measurements, when the sign was greater than 2 volts, it introduced distortion. At 3 volts there was 10% distortion. At 5 volts there was about 20% distortion. On a guitar this may be desirable or in a noisy night club show where you won’t hear the distortion, but in a church, the distortion can be very unpleasant. As long as the sign stays below 2 volts, this transformer will do a reasonable job.

The other unit converts Mic Levels to Line Levels. The performance of these units were bench tested with a MLSSA (a computerized audio and acoustical testing system) and the performance was surprisingly very good. The limiting factor is voltage. The unit with the Female XLR to Male ¼ inch connectors can not handle a load much higher that 1 volt of power. At 1 volt the transformer saturates and it sound horrible. Any signal below 1 volt will have a frequency response from 10 hertz to 20,000 hertz ±1.5dB. The transformer is down 6dB at 3 hertz. From 50 hertz to 15,000 hertz the unit is ± .25dB. In my books, this is an excellent performance for most smaller church needs. The best function for this transformer is in trapping RF signals for mixers that do not have good quality electronically balanced inputs (Some mixers have transformer inputs which traps RF.)

Update 1997.

Recently on the news groups, there was some mis-information being shared which I feel should be corrected. A person posted the question, “Can an active DI boost the signal from -20dB to +0dB. I want to boost the signal of my acoustic guitar pickup.”

The response to this question was remarkable. What was very surprising was when I saw who was answering the questions.

First of all, lets look at the question. – The request was to know if an active DI can boost an audio signal from -20dB to +0dB. First of all, we should know what -20dB means.

In HI-FI, -10 and -20dB is the standard used to connect from stereo equipment to equipment. Part of the reason for this standard is that a lower signal has few problems with noise from RF and HUMs and at that level, it is cheaper to provide RF protections at -10dB. However, this signal is too low to manipulate for editing without adding noise that is inherent of all audio equipment and signals – even digital signals.

In Pro Audio, we use +4 as a standard. Part of the reason (among other things) for this higher output is to boost the signal high enough for a greater signal to noise ratio. Let me explain. A line level to line level signal often already has a signal to noise ratio of 60dB or more. A microphone can have a signal that is from – 80dB to +10dB. That is 90dB of dynamic range. If the low level -80dB signal is clean – that is little or no noise, by boosting it to +4dB means that when you split the signal for monitors, effects and recording outputs, when you change the signal with the channel EQ and then send the signal out of the mixer, your original signal should be (almost) noise free. (If you have a cheep mic, that can often be a problem when micing a person’s voice at a distance.) In otherworldly, the hotter the signal, the better for Pro Audio- and all church sound system come under this label.

As a side bar. – Have you even connected a CD player directly to a Pro Amplifier and found that you could turn the CD up all the way without clipping the amplifier? It’s because the maximum output of most consumer CD player are .75 Volts – which is the maximum output of a HIFI product. For Pro Audio – many pro amplifier are 1.75 volts (+4dB) or 2.83 volts (+8dB). This voltage difference and signal difference is the main reason why you can not mix HIFI and Pro Audio equipment. (Note, some lower prices Pro audio amps have switches for .75 volts for consumer use.)

Back to the Question – Many active DI boxes have switches that can cut a signal down. Most Active DI boxes have 0dB, -10dB and -20dB. Some DI boxes also have -45dB. These are pads. Pads are loads created with resistors and other components to cut the signal down when the input voltage is too high. A passive DI box will loose between 3 to 6dB of signal. For many sound sources, this is OK. Also, passive DI use transformers. All transformers have a unique sound. If your church has an NC above 42dB, the sound of the DI will not be noticeable. If the church has an NC below 42dB, then everything counts.

Active DI boxes offer 0dB signal loss and since they don’t use transformers, they add far less coloration to the original sound. In order for a Direct Box to Boost a -20dB signal to +0dB, you need internal amplifiers like a mixer has. To the best of my knowledge, there are only a few Active DI boxes that have such abilities. Generally, they should be called Active DI with Preamps. Most of the common Active DI boxes do not have this ability.

These DI boxes with pre amps and gain controls built in require 24 volts or more to boost a signal. A full boost of signal can be achieved with a 48 volt phantom power supply as supplied in many pro quality mixers. Some of these DI’s can boost a signal to +20dB, but doing this without gain noise is remote. In a club with 55dB of background noise this probably isn’t a problem – in a church with 40dB of background noise and preamp noise will be a major issue.

The solution for the guitar player is to use a guitar foot pedal pre amp that can also add Bass, mid and treble tone controls – then go into a DI box. The signal will be boosted before going into the DI box – as it should.

For other low level signal, you can use a Guitar pre amp or- you can use a unit like the Symetrix 202. It is a two channel pre amp with phantom power. It can be used as a mixer by itself or to boost a low level signal. It can handle almost any kind of input and convert it to 600 ohm balanced load. You don’t need a DI box with this unit. it has a ground switch, a pad, a gain control and phase switch. Because it has two channels, you can mix two sounds, like a mic and guitar before sending it to the main mixer, or mix 2 acoustic guitars. The option is yours.

What prompted this writing is the fact that well known audio experts are either telling people that any active DI box can boost a signal, or they are accepting this info as fact. Yes, there are some active DI boxes that have a built in line amplifier to increase the signal which makes these unit more than a pure active DI and if you read the product label, it will tell you if there is a line amp included.

In summary, a DI box should always be used as your first choice when connecting an electronic instrument to a sound system where you are using mic cables over 50 feet to the mixer. Use the in line transformers sparingly, especially if your don’t know the output voltage. And yes, with practice, in 30 minutes you can connect up to 24 mic inputs with two people and finish a sound check. Check DI 1, DI 2, DI 3……

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DI Box FAQ

Question from those who search the web.

Can you use a DI box with a mic? Jan 2012

The short answer is – NO.

The long answer is – DI boxes are not pre amps or mic signal amplifiers. They are passive devices. Even an Active DI box is passive. All it does is give you better control of the input sign to prevent clipping of a hot signal. Di Boxes convert one type of signal to another. That said, there are a few expensive boxes that are suppose to work both as a DI box and as a preamp for line level signal. They can not be used to manage mic level signal whether balanced or unbalanced. DI boxes are 1/4 inch inputs and XLR and 1/4 inch outputs. When they say preamp/DI box, what they are saying is that they can change the bass, treble, mids and add sound effects to the hot signal and then send it to the mixer at mic level or line level for a Guitar amp.

If you are looking to boost a mic signal, you need a pre-amp and they are many phantom powered, battery powered, USB powered and DC/AC wall wart powered pre-amps.

Can you connect from a Mixer to an Amp Directly?

The Short Answer is – Yes

The Long Answer is – Amp inputs are line level. HIFI/Consumer products connect at -10dB. Pro products are setup for +4dB. The key here is to have the proper type of cable connections. It is best to run from XLR to XLR or TRS to TRS or TS to TS. If you have to go from XLR or TRS to TS, and you are having any hum issues then a DI box will help you out and correct the grounding issues.

What is the best way to connect from a computer or Laptop or Ipod/Iphone/Ipad to a mixer for music playback?

The proper way to take a headset signal output to a single mixer input is to connect with two Line Match Transformers. You need a transformer for both the Left and Right channel. Why? One of the sacred rules in audio is that you can split or “Y” an output signal to two devices but never combine or “Y” an input signal to the input of a mixer. In many churches there are Cassette players, MP3 players, CD players and other playback devices that have only one channel working. When you “Y” an output to a single connection, you are creating an improper load and that often leads to a Left or Right channel being burned out over time. There are summing boxes that you can use but they can be expensive. Better yet, if you have two free input channels or you have stereo input channel use them. If you only have 1 channel, the line match transformers will protect the mix and the playback device.